1------------------------------------------------------------------------------
2--                                                                          --
3--                         GNAT RUN-TIME COMPONENTS                         --
4--                                                                          --
5--                       S Y S T E M . E X N _ I N T                        --
6--                                                                          --
7--                                 B o d y                                  --
8--                                                                          --
9--          Copyright (C) 1992-2009 Free Software Foundation, Inc.          --
10--                                                                          --
11-- GNAT is free software;  you can  redistribute it  and/or modify it under --
12-- terms of the  GNU General Public License as published  by the Free Soft- --
13-- ware  Foundation;  either version 3,  or (at your option) any later ver- --
14-- sion.  GNAT is distributed in the hope that it will be useful, but WITH- --
15-- OUT ANY WARRANTY;  without even the  implied warranty of MERCHANTABILITY --
16-- or FITNESS FOR A PARTICULAR PURPOSE.                                     --
17--                                                                          --
18-- As a special exception under Section 7 of GPL version 3, you are granted --
19-- additional permissions described in the GCC Runtime Library Exception,   --
20-- version 3.1, as published by the Free Software Foundation.               --
21--                                                                          --
22-- You should have received a copy of the GNU General Public License and    --
23-- a copy of the GCC Runtime Library Exception along with this program;     --
24-- see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see    --
25-- <http://www.gnu.org/licenses/>.                                          --
26--                                                                          --
27-- GNAT was originally developed  by the GNAT team at  New York University. --
28-- Extensive contributions were provided by Ada Core Technologies Inc.      --
29--                                                                          --
30------------------------------------------------------------------------------
31
32package body System.Exn_Int is
33
34   -----------------
35   -- Exn_Integer --
36   -----------------
37
38   function Exn_Integer (Left : Integer; Right : Natural) return Integer is
39      pragma Suppress (Division_Check);
40      pragma Suppress (Overflow_Check);
41
42      Result : Integer := 1;
43      Factor : Integer := Left;
44      Exp    : Natural := Right;
45
46   begin
47      --  We use the standard logarithmic approach, Exp gets shifted right
48      --  testing successive low order bits and Factor is the value of the
49      --  base raised to the next power of 2.
50
51      --  Note: it is not worth special casing base values -1, 0, +1 since
52      --  the expander does this when the base is a literal, and other cases
53      --  will be extremely rare.
54
55      if Exp /= 0 then
56         loop
57            if Exp rem 2 /= 0 then
58               Result := Result * Factor;
59            end if;
60
61            Exp := Exp / 2;
62            exit when Exp = 0;
63            Factor := Factor * Factor;
64         end loop;
65      end if;
66
67      return Result;
68   end Exn_Integer;
69
70end System.Exn_Int;
71